Onion Growth and Bulb Enlargement Cultivated in Gray Lowland and Andosol Soils

Abstract

A spring-sown onion trial was conducted in different soil areas in the same geographical area. The harvest date of onion grown in gray lowland soil was four to ten days earlier than that in andosol, depending on the onion variety. Throughout the study period from seedling to harvest, plants in the lowland area showed vigorous growth in height and number of leaves before bulb enlargement, and bulb enlargement in the lowland area was earlier than in the andosol area. In addition, the average daily soil temperature in the lowland area during the mid-growth stage in June was high. ANOVA was conducted for the year of cultivation and soil treatment of ‘Momiji No. 3’, which revealed that the lowland area significantly influenced the increase in bulb weight and bulb diameter. Furthermore, considering the physical properties of soil, the lowland had higher bulk density and solid phase distribution than andosol. The distribution of the liquid phase was higher in andosol, indicating that the moisture content was higher in this soil type. It was hypothesized that the higher moisture content in andosol prevented an increase in soil temperature by evaporation, resulting in growth differences. While this study investigated the influence of environmental factors such as soil variation and meteorological data on crop growth, future research should focus on both environmental and genetic factors to fully clarify the onion bulb enlargement process.